1. Field of the Invention
This invention relates to an intake control valve device used in an internal combustion engine.
2. Related Art
For example, JP-A-56-115818 discloses a multi-cylinder internal combustion engine in which an intake control valve of the butterfly type is provided within a surge tank to divide the interior of this surge tank into a first internal chamber and a second internal chamber. When the valve is fully opened, the two internal chambers are caused to communicate with each other so as to change an equivalent tube length of an intake passage, thereby achieving a high charging efficiency over an entire engine speed range, utilizing an intake inertia effect.
In an intake valve device used in this kind of internal combustion engine, if there is even a slight air leakage when an intake control valve is fully closed, the intake inertia efficiency is lowered, so that the charging efficiency can not be sufficiently enhanced. Therefore, the intake valve device is required to have a high sealing effect.
In order to enhance the sealing effect in the fully-closed condition, there has been proposed a valve device (as disclosed in JP-A-03-286152 and JP-U-60-69339) in which a body, housing the valve therein, has a valve seat surface of a stepped configuration, against which an outer peripheral portion of an upstream-side surface in one half of a circular portion of the valve can abut in the fully-closed condition of the valve, and another valve seat surface of a stepped configuration against which an outer peripheral portion of a downstream-side surface of another half of a circular portion of the valve can abut in the fully-closed condition of the valve.
This conventional valve device will now be described with reference to FIGS. 5 and 6.
FIG. 5 shows the valve device disclosed in JP-A-03-286152. A valve shaft 103, which can be rotated by opening-closing control means, extends through an exhaust passage 102 in a body 101, and a butterfly-type valve 104 is fixedly mounted on the valve shaft 103. A valve seat surface 106 of a stepped configuration, against which an outer peripheral portion 105 in one half of a circular portion of the valve 104 can abut in the fully-closed condition of the valve 104, is formed in an inner peripheral surface of the body 101 generally over a half of the periphery thereof. A valve seat surface 108 of a stepped configuration, against which an outer peripheral portion 107 of another half of the circular portion of the valve 104 can abut in the fully-closed condition of the valve 104, is formed in the inner peripheral surface of the body 101 generally over a half of the periphery thereof. The angle .theta..sub.1 of each of the two valve seat surfaces 106 and 108 (in the rotating direction of the valve) with respect to a plane perpendicular to the axis of the exhaust passage 102 is equal to the angle .theta..sub.2 of inclination of the valve 104 in its fully-closed condition. In order to enhance the sealing effect, opposite ends (edges) 109, 110 of each of the two valve seat surfaces 106 and 108 in the direction of the periphery thereof are formed close to the proximal portions of the valve shaft 103, respectively.
FIG. 6 shows the valve device disclosed in JP-U-60-69339. In the valve device, two semi-cylindrical sleeves 202 and 203 are mounted on an inner peripheral surface of a body 201, and the two valve seat surfaces 106 and 108 of a stepped configuration, shown in FIG. 5, are formed by end surfaces 204 and 205 of the two sleeves 202 and 203, respectively. The angle .theta..sub.1, of each of the two valve seat surfaces 206 and 207 (formed respectively by the end surfaces 204 and 205) with respect to the perpendicular plane to the axis of the exhaust passage is equal to the angle .theta..sub.2 of inclination of the valve 208 in its fully-closed condition. Opposite ends (edges) 209, 210 of each of the two valve seat surfaces 206 and 207 are formed close to proximal portions of a valve shaft 211, respectively.
Incidentally, there are dispersions in the machining precision and assembling precision of the above valve, valve shaft and valve seat surfaces, and besides these parts are subjected to thermal strain deformation due to a temperature change.
Therefore, in the above construction in which the angle .theta..sub.1 of each of the two valve seat surfaces 106 and 108 (206 and 207) is equal to the angle .theta..sub.2 of the valve in its fully-closed condition, and the opposite ends (edges) 109, 110 (209, 210) of each of the two valve seat surfaces 106 and 108 (206 and 207) are formed close to the proximal portions of the valve shaft 103 (211), respectively, there is a possibility that before the valve 104 (208) is fully closed, the valve 104 (208) and the proximal portions of the valve shaft 103 (211) interfere with the ends (edges) 109 and 110 (209 and 210) because of dispersions in the machining precision and assembling precision and the thermal strain deformation, and as a result the valve 104 (208) is prevented from further rotation, so that the valve fail to be completely seated on the valve seat surfaces, thus lowering the sealing effect.